The subject matter disclosed herein relates to electric motors, and more particularly to synchronous electric machines having multiple inverters, as well as a method for routing power to such electric motors.
A number of pulse-width modulation (PWM) inverters have been developed for converting direct current (DC) power or fixed frequency alternating current (AC) power to variable frequency AC power for the purpose of driving large AC synchronous motors at variable speeds. The use of such PWM inverters allows operation of higher rating motors incorporating conventional lamination and conductor types by attaching a polyphase, such as a 3-phase, inverter to each of two or more 3-phase stator windings to achieve high system power ratings.
Despite adequate performance by the PWM inverters in such applications, relatively minor voltage differences between the inverter outputs is often present due to sampling errors, timing errors or current regulator activity, for example. Although the voltage differences are typically present for a relatively short amount of time, such as a few microseconds, the voltage differences drive stray flux through the rotor laminations of the synchronous motor. The stray flux generates currents in the laminations that ultimately may lead to loosening of amortisseur bars in a rotor and subsequently may result in damage to various components, such as the stator, for example, and in extreme cases an overall system failure.